Distribution of powder for making coated glass

ABSTRACT

A process for the distribution of a powder for coating glass, whereby a regular, homogeneous coating of uniform thickness is formed, wherein the powder is converted into a metal oxide or oxides upon contact with hot glass, which comprises spraying a powder onto said glass, wherein said powder comprises: (a) a composition which is capable of being converted into a metal oxide or oxides upon contact with hot glass, and (b) a water-repellent, anhydrous product having a base of finely-divided silica. 
     The product with a base of finely-divided silica is added in the amount of about 0.5 to 5%, by weight, based on the total powder weight.

This is a division of application Ser. No. 06/519,710 filed on Aug. 2,1983, now U.S. Pat. No. 5,004,503.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the distribution of powder products andrelates more particularly to the coating of glass with a layer of metaloxides obtained by pyrolysis of a powder of organometallic compoundssprayed on the glass at high temperature.

2. Description of the Prior Art

When glass is to be coated with a layer of oxides such as the oxides ofFe, Cr, Co, Ti, Al, Sn or Cu, for reflecting solar heat radiation,tinting, or increasing the hardness of the glass articles, dishes, orbottles, for example, the glass is often sprayed with a solutioncontaining organometallic compounds that can be transformed into metaloxides at high temperature.

However, this process exhibits drawbacks. In particular it produceslayers with irregular metal oxides and, moreover, cools the glass toomuch. This is particularly bothersome for thin glass which can bebroken. Such a process also requires the use of solvents that may beharmful, or which are flammable or which are expensive.

To avoid these drawbacks, attempts have been made to spray the glassdirectly with powdered metal rather than with a solvent containing themetal compounds.

In the attempt to achieve a homogeneous distribution of the sprayedpowder over the entire surface of the glass, it is known from Patent EP6064 that the powder may be distributed on the glass with a devicecomprising a distribution slot placed over the entire wide width of theglass strip passing under it, with the slot being preceded by a primaryslot which is fed powder by a multiplicity of pipes.

The process and device of EP 6064 have made it possible to avoid some ofthe drawbacks associated with the spraying of a solution and haveimproved the quality of the coated products so manufactured. However,when it is desired to increase the treatment width, for example, when itis desired to coat glass ribbons 4 m wide, or when it is desired toreduce the delivery of carrier gas to cool the glass less to obtain astill higher pyrolysis efficiency, or when it is desired to obtain eventhinner and more homogeneous coatings, new difficulties are encountered.For example, the powder of the organometallic compounds adheres to thewalls of the pipes that are carrying it and accumulates on the pipewalls. This can result in altering the delivery of powder and thereforethe quality of the coating.

Further, only a relatively slight resistance of the deposited metaloxide layers to chemical agents can be noted, perhaps due to the hightraveling speed of the substrates to be coated under the powderdistribution slot.

Therefore, a need continues to exist for a process which distributespowders in regular, homogeneous coatings having uniform thickness, whichare resistant to chemical attack, such that the devices employed todistribute the powders do not become clogged with the powders as thepowders are distributed.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide aprocess for the distribution of a powder in regular, homogeneouscoatings.

It is also an object of the present invention to provide a process forthe distribution of a powder in regular, homogeneous coatings whereinthe coating so produced is resistant to attack by chemical agents.

Further, it is also an object of this invention to provide a process forthe distribution of a powder in regular, homogeneous coatings havinguniform thickness.

Moreover, it is a particular object of the present invention to providea process for the distribution of a powder in regular, homogeneouscoatings on glass, wherein a coating of uniform thickness is attained,and wherein the delivery of carrier gas for the powder to the glasssurface is reduced, to allow less cooling of the glass, therebyimproving the pyrolysis efficiency of the glass.

According to the present invention, the foregoing and other objects areattained by providing a process for the distribution of a powder forcoating glass, whereby a regular, homogeneous coating of uniformthickness is formed, wherein the powder is converted into a metal oxideor oxides upon contact with hot glass, which entails spraying a powderonto the glass, wherein the powder contains (a) a composition which iscapable of being converted into a metal oxide or oxides upon contactwith hot glass, and (b) a water-repellent, anhydrous product having abase of finely-divided silica.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This invention contemplates increasing the utility of the coatingprocess using powders, while avoiding the operating difficultiesmentioned above. Moreover, it also contemplates providing coatedsubstrates exhibiting good properties, in particular, substrates havingregular and homogeneous coatings and resistance to attack by chemicalagents.

For this purpose, the present invention proposes to add water-repellent,finely divided silica-base products to the powder that is to be sprayedon the glass.

These products should contain a high percentage of silica, equal to orgreater than 90%, preferably at least on the order of 98% with no oronly slight impurities that can pollute the coating film.

These products are advantageously formed of particles whose average sizeis on the order of 1/1000 of the size of the grains of powder to besprayed on the glass.

Thus, for powders from a micron to some dozen microns of average size,products having particles on the order of 7 to 20 nanometers, preferably10 to 15 nanometers (nm), in average size are suitable. More precisely,the product sold under the commercial name AEROSIL R 972 containing frommore than 98.3% cf SiO₂, having particles of an average size of 16 nm,an apparent density of 50 g/1 and a given surface according to thestandardized measurement B.E.T. of 120+30 m² /g is suitable.

The silica-base products sold under the tradenames CABOSIL and TIXOSILare also suitable for use according to the present invention.

The powder which is to be sprayed on the glass contains (a) acomposition which is capable of being converted into a metal oxide oroxides upon contact with hot glass, and (b) a water-repellent, anhydrousproduct having a base of finely-divided silica.

The composition (a) which is capable of being converted into a metaloxide or oxides upon contact with hot glass may be organometallics suchas dibutyltin difluoride, dibutyltin oxide, acetylacetonates of variousmetals such as Fe, Cr, Co, Ti, Al, Sn, Cu or In or a mixture thereof.Other compounds of the metals Fe, Cr, In, Co, Ti, Al, Sn, Cu or mixturesthereof, which similarly are converted to a metal oxide or oxides uponcontact with hot glass may also be used.

The water repellent, anhydrous product having a base of finely-dividedsilica is present in the amount of 0.5 to 5% by weight, based on thetotal powder weight. It is preferable, however, that the product havinga base of finely-divided silica is present in the amount of 1 to 2% byweight, based on the total powder weight. In large proportions, anunfavorable effect is noted with respect to the regularity andhomogeneity of the powder distribution. Additionally, percentages of thefinely-divided silica base product in excess of 5% result in asubstantial change in the optical properties, for example, of thecoating produced.

The present invention will be further illustrated by certain examplesand references which are provided for purposes of illustration only andare not intended to limit the present invention.

Tests were run with various powders, to determine the percent by weightof the silica-base products that should be added to the powders toprevent clogging of the devices and to regulate powder distribution,without, however altering the properties, particularly the electricaland optical properties and resistance to attack by chemical agents, ofthe deposited layers.

EXAMPLE 1

Testing was conducted on powder mixtures of 70% iron triacetylacetonateand 30% chromium triacetylacetonate having no "Aerosil" added, and onthe same mixture of iron and chromium triacetylacetonates but with 0.5,1.0, 1.5, 2.5 and 10% by weight of added "Aerosil".

For this purpose, a mixture of iron triacetylacetonate and chromiumtriacetylacetonate, mixed in the proportion of 70:30, respectively, wasdehydrated for 24 hours at 60° C. whereby the water content decreased to0.5%. This mixture was then crushed in a grinder so that the crushedpowder had a granulometry of 3 to 25 microns. An average grain diameterof 7 to 8 microns was selected for testing.

Seven identical samples of this mixture were prepared and to these wereadded the amounts of "Aerosil R 972' listed above, i.e., 0, 0.5, 1.0,1.5, 2.0, 5.0 and 10.0% by weight. Each sample was mixed for threeminutes and then each of the seven samples was then subjected to testingwith the device shown in described herein.

This device comprises a hopper provided at its lower end with an endlessscrew distribution system, an iron plate sloped 60° and placed at thefoot of plate.

Each of the samples, weighing 10 grams and introduced in into the hopperone after the other, was distributed onto the plate and the powderrecovered in the container was, weighed; the difference between theamount of powder introduced into the hopper and the amount of powderrecovered gave an indication of the ability of the powder to adhere tothe plate, and therefore its lack of ability to flow. In this figure,the amount of powder that remained the A considerable drop in theadherence of the powder to the was noticed when the percentage of"Aerosil" increased from 0 to 2%, then after 2% of addition, theadherence still decreased slightly to an addition of 5%, then itremained stable.

This test measured the ability of the powder to adhere to the pipes and,consequently, its inability to be distributed by powder distributioninstallations.

The different powder mixtures produced in Example 1 were then utilizedin the manufacture of coated substrates in Example 2.

EXAMPLE 2

Samples of the same iron triacetylacetonate and chromiumtriacetylacetonate were used, to which 0%, 0.5%, 1% and 2%,respectively, of "Aerosil" were added to test the coatings obtained fromthese various samples for resistance to attack by chemical agents.

The powder of the four samples was successively sprayed with a gun onthe surface of glass plates 5 mm thick and 150 mm×150 mm in size,brought to a temperature of 575° to 580° C. The air pressure entrainingthe powder in the gun was 4.5 kg/cm² and the delivery was 80 1/min. Inall cases, the spraying lasted 2 seconds. Thus, glass regularly coatedwith a layer of Fe and Cr oxides was obtained. The samples were cut into50 mm×25 mm test pieces which were immersed in baths of hydrochloricacid (HCl) and sodium hydroxide (NaOH) of a normality of 1. A count wasmade of the number of days at the end of which a defect of the pinholetype, fading, detachment occurred on the coatings.

The results are given in Table 1.

                  TABLE 1                                                         ______________________________________                                               Amount (%)                                                                    of Aerosil                                                                    (SiO.sub.2) in                                                                         Number of days of endurance                                            powder to  resistance to                                                                            resistance to                                  Sample No.                                                                             be sprayed acid       sodium hydroxide                               ______________________________________                                        1        0%         8      hours  9 days                                      2        0%         8      hours  9 days                                      3        0%         8      hours 12 days                                      4        0.5%       1      day   14 days                                      5        0.5%       1      day   12 days                                      6        0.5%       3      days  19 days                                      4        1%         3      days  27 days                                      5        1%         2      days  17 days                                      6        2%         5      days  29 days                                      7        2%         11     days  19 days                                      8        2%         9      days  17 days                                      ______________________________________                                    

Inspection of Table 1 indicates that the resistance of the coatings toattack by acids or bases increases with increased content of "Aerosil"in the coating.

EXAMPLE 3

Tests were also run on mixtures of powder of 50% iron triacetylacetoneand 50% chromium triacetylacetone, in a stage without addition of finelydivided silica, in a second state with addition of 1% silica, then in athird stage with addition of a percentage of silica greater than 5%.

It was found that the distribution of the powder mixture is greatlyimproved when 1% of finely divided silica has been added; the powderdelivery is increased and the regularity of the distribution isimproved.

On the other hand, it was found that for additions of a percentagegreater than 5%, there is no additional improvement on the distributionlevel, but that the properties of the coatings obtained on the glass,particularly the optical and electrical properties, are changed.

The same findings were made with dibutyltin difluoride, dibutyltinoxide, acetylacetonates of various metals (Fe, Cr, Co, Ti, Al, Sn, Cu,In) of mixtures of various metal acetylacetonates (for example, Fe, Cr,Co^(II)) and of various other compounds of the metals Fe, Cr, In, Co,Ti, Al, Sn, Cu or mixtures of these powders.

Finally, it was found that the improvement made by addition of finelydivided silica is slight when the amount added is 0.5%, and it ismaximal for doses of 1 to 2%, and in particular 2%. Percentages higherthan 5% result in an alteration of the coating properties.

Addition of finely divided, anhydrous, water-repellent silica thereforemakes it possible to improve the distribution of the powder. It promotesthe use of longer distribution slots while preserving the regularity andhomogeneity of the distribution.

With the homogeneity and regularity of the powder distribution beingimproved, it is now easier to make coatings on glass, particularlycoatings having electrical properties, and of these coatings, antistaticcoatings, in particular. The difficulty in obtaining a continuity of thecoating, without localized excess thicknesses that result in consumptionof powder and alter the optical properties, particularly transmission,is known. Because of the surprisingly improved homogeneity andregularity of powder distribution, it is possible to obtain layers ofmore regular coating, or more uniform thickness. This is particularlyimportant in the case of antistatic layers when a continuity of thecoating is desired, concurrently with a slight thickness to attainelectric resistances on the order of 100,000 ohms per square.

The homogeneity and regularity of powder distribution is also reflectedby a more beautiful appearance of the coatings, without speckling andwithout causing irritation phenomena.

It was also found that resistance of the coatings to abrasion is morehomogeneous and that resistance to attack by chemical agents isenhanced.

It is also known that it is very important to control the granulometryof the sprayed powders to avoid their toxicity with respect to thetechnicians making the coated glasses. Due to the addition of finelydivided, water-repellent silica, reagglomeration of the powders isavoided, and a constant granulometry is obtained which is selected toavoid any toxicity.

With the powder distribution improved, it is possible to reduce thedelivery of carrier gas to the glass, thereby reducing the cooling ofthe glass. This cooling of the glass is caused by spraying of powder insuspension in the carrier gas, and the avoidance or minimization thereofis an advantage when tempered coated glasses are to be produced. It isknown that it is difficult to obtain pyrolysis of the powder of anorganometallic compound sprayed on glass with a satisfactory pyrolysisefficiency without bringing the glass to a temperature above about 520°C. in order to prevent the disappearance of surface compression stressesof the glass, resulting from tempering. With the glass, therefore,initially being relatively cold, an effort is made to lower itstemperature as little as possible by spraying. The use of powders,particularly dibutyltin oxide, described in French Patent Publication2,391,966, illustrated some progress with respect to the use of metalcompounds in solution. However, it is now possible to reduce delivery ofthe carrier gas acting as a vehicle for the powder, due to the additionof water-repellent, finely divided silica. This constitutes asignificant improvement over known coating processes and now makes itpossible to cool the glass even less and thereby improve the pyrolysisefficiency.

The additives introduced in the powders according to the presentinvention have a favorable effect on the coated powders with thepreferred proportions being between 0.5 and 5% and preferably between 1and 2%. In larger proportions, an unfavorable effect is noted withrespect to the regularity and homogeneity of the distribution of thepowders, and also with respect to the contamination of the coatings,with the optical properties, in particular, being disturbed.

To make possible a good covering of the powder grains by particles offinely divided water-repellent silica, the powder is added in increasingfractions in a container or is mixed with all the finely divided silicathat is to be incorporated.

Having now fully described this invention, it will be apparent to one ofordinary skill in the art that many changes and modifications can bemade thereto without departing from the spirit or scope of the inventionas set forth herein.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:
 1. A coated glass with enhanced resistance toattack by chemical agents, and having a regular, homogeneous coating ofuniform thickness, which is produced by a process comprising spraying apowder mixture onto hot glass, said powder mixture comprising:a) acomposition which comprises dibutyltin difluoride, dibutyltin oxide, theacetylacetonates of Fe, Cr, Co, Ti, Al, Sn, Cu or In, or a mixturethereof, or other compound of the metals Fe, Cr, In, Co, Ti, Al, Sn orCu or a mixture thereof which are capable of being converted into ametal oxide or oxides upon contact with hot glass, and b) awater-repellant anhydrous product having a base of finely-dividedsilica, wherein the proportion of product (b) added is between about 0.5to 5%, based on the total weight of the powder, and further wherein theaverage granulometry of the composition (a) is in the range of one toseveral dozen microns, and the average granulometry of the product b) isin the range of 7 to 20 nanometers.
 2. The coated glass of claim 1,wherein said coating is an antistatic coating having an electricresistance of approximately 100,000 ohms per square.
 3. The coated glassof claim 1, wherein the average granulometry of the product (b) is inthe range of 10 to 15 nanometers.
 4. The coated glass of claim 1,wherein the product (b) is finely-divided silica containing at least 98%silica.
 5. The coated glass of claim 1, wherein the proportion ofproduct (b) added is between about 1 and 2%, based on the total weightof the powder.
 6. The coated glass of claim 1, wherein the composition(a) is dibutyltin difluoride, and product (b) is a finely-divided,water-repellent silica, wherein the water-repellent silica comprises 2%by weight of the total powder weight.